The present invention relates to a pneumatic booster, and more particularly to a vacuum brake booster for an automotive vehicle comprising basically a casing having at least one movable wall disposed therein dividing the casing into two chambers, with the differential of pressure between a low pressure in one of the two chambers and atmospheric pressure in the other of the two chambers acting on the movable wall providing the boosting effect. The movable wall includes at least one rigid diaphragm plate and one flexible diaphragm. A pneumatic booster of the above-mentioned type is disclosed in German patent DE-OS No. 2,808,622. Another pneumatic booster of the above-mentioned type is disclosed in a copending application of P. Reidel and L. Haar, Ser. No. 143,384, filed Apr. 24, 1980, whose disclosure is incorporated herein by reference.
The known vacuum brake boosters are unable to comply with the vehicle manufacturers' demands for a lowest possible weight of brake systems without the safety and operability of the devices being impaired. Several proposals have been made with respect to the weight reduction of vacuum brake boosters, which would, however, necessitate a complete reconstruction of the brake booster.